The 75-year old priest was airlifted back to his home country on Thursday along with a nun who tested negative for the disease. Over the weekend the priest had been treated with the untested drug, Zmapp, which the World Health Organization today gave the green light for health authorities to use.

The virus is now so virulent it has killed over 1,010 people in Liberia, Sierra Leone and Guinea. It is rare for the World Health Organization to approve the use of drugs when the side effects and efficacy have yet to be proven.

The priest was working in the Liberian capital, Monrovia and was part of a Catholic Church mission that worked at the local Hospital of St. Joseph. The hospital has since been closed down after a nun from The Congo died there on Saturday. Last week, the hospital administrator and director, Joseph Nshamdze, also died.

Why So Virulent - What is Ebola?

Ebola is a viral condition where initial symptoms can see instant and sudden fever, intense weakness, muscular pain and a sore throat, according to the World Health Organization (WHO). Those affected by the virus will suffer these symptoms only in the first stages of the illness. Later patients will be vomiting, suffering from diarrhoea and could see both internal and external bleeding.

The disease reaches humans after close contact with infected animals, including chimps, fruit bats and antelopes. Then when humans directly contact other humans via bodily fluids or infected blood, the disease spreads. Even touching a dead person with Ebola can be a risk.